www.ijecs.in International Journal Of Engineering And Computer Science ISSN:2319-7242 Volume 2 Issue 11 November, 2013 Page No. 3250-3255

Sree Vardhan IJECS Volume 2 Issue 11 November, 2013 Page No. 3250-3255 Page 3250

DC/DC Boost Converter Functionality in a Three-Phase IMC

Sree Vardhan, S.V. Panidhar

Abstract—An indirect matrix converter (IMC) connected with two input power sources is proposed: a gasoline generator

as themain ac power supply and batteries as the secondary power source. The IMC is small in size because of having a dc-

link part without an electrolytic capacitor. The dc-link part is utilized by connection with a boost-up chopper with

batteries as a secondary input power source. Furthermore, the chopper connects to the neutral point of the motor and

utilizes the leakage inductance of the motor as a reactor component. The proposed technique successfully further reduce

the size of the converter by removing the boost reactor in the boost converter stage. The proposed converter is simulated

and experimentally validated using a 750-W prototype and an induction motor driven with V/f control. The total harmonic

distortion of the input and output currents are 4% and 3.7%, respectively,and the efficiency is 96%

Index terms—Synchronous Reference Frame,

instantaneous current component theory, Modified SRF,

Active Filter, Harmonics.

I. INTRODUCTION

Environmental responsibility has become a significant

concern for communities so that the development of

renewable power sources, such as wind turbines and low-

carbon emission hybrid electric vehicles (HEVs) is

progressing rapidly. One of the most common applied

converters in hybrid systems is the ac/dc/ac converter

because it has the ability of connecting to two different

power sources. The generator mainly supplies constant

power to the load and a battery is used as an alternate power

source to drive an electric motor and also to absorb the

power fluctuation during periods of high peak energy

demand. Fig. 1 shows a conventional ac/dc/ac power

converter, which typically consists of a pulse width

modulation (PWM) rectifier, a dc-link capacitor, and a

PWM inverter, also known as a back to- back (BTB) system

[1]–[3]. The PWM rectifier is often used to reduce the

harmonic currents in a generator and control the dc-link

voltage [2], [4]–[6]. In order to obtain high performance

under an adjustable speed drive system, a constant dc-link

voltage is required in a BTB system because the voltage

fluctuation of the dc-link part will cause an output voltage

error. A typi- cal method for reduction of the voltage

fluctuation is to place a large electrolytic capacitor into the

dc-link part as a filtering device between the rectifier and

the inverter. However, a large

electrolytic capacitor is bulky

Another approach is to reduce the capacity of the

electrolytic

capacitor by the application of a high-speed dc-voltage

controller to the rectifier control [7]. However, the control

response is limited by the delay of the voltage detection and

digital controller; therefore, the electrolytic capacitor is still

required. In addition, the capacitance is not reduced, since

the dc-link capacitor is dominated by the capacitor current.

As a result, a large amount of space is required for the

capacitor installation in a practical device. In addition,

electrolytic capacitors are not suitable for high-temperature

applications, such as in HEVs. Overall, these disadvantages

of the electrolytic capacitor affect the reliability of the

converter.

.

Fig. 1: Back-to-back converter.

For the secondary input power source, a boost converter that

consists of a boost reactor and a switching leg [insulated

gate

bipolar transistor (IGBT)] is connected with batteries to the

dclink part of the BTB system. Boost converter will control

the

battery current and the battery power will be used as a

secondary power to drive the electric motor. In this paper, a

new circuit topology is presented, which is composed of an

indirect matrix converter (IMC) and a dc/dc boost converter

that connects to the neutral point of a motor. An IMC has

high efficiency and is easily configured in comparison to

matrix converters [8]–[12]. In addition, this converter does

not require a dc-link electrolytic capacitor to filter the dc-

ripple voltage. It uses a direct conversion technique where

the frequency of the dc-link voltage contains a ripple with

Sree Vardhan IJECS Volume 2 Issue 11 November, 2013 Page No. 3250-3255 Page 3251

six times of the input frequency. However, the output

voltage transfer ratio is limited by this direct conversion

technique which is similar to the matrix converter, where

output voltage = 0.866 of the input voltage [13].1)

Where x denotes voltages or currents.

Fig. 2: Proposed scheme

Nevertheless, an appropriate control over the inverter is also

proposed so that it is possible to connect a dc chopper to the

neutral point of the motor and to operate as a dc/dc

converter [14]. This dc/dc converter with a battery is

performed as a secondary power source of the IMC to drive

the electric motor. The proposed circuit utilizes the neutral

point of a motor in the boost converter because the leakage

inductance of the motor can be used as a reactor. Generally,

the leakage inductance is around

10% of the rating impedance in an induction motor. For the

proposed dc converter, around 3% of the reactor is enough

to use

as a boost reactor component. Please note that the

synchronous

reactance in a permanent motor is higher than the leakage

inductance of an induction motor. By removing the

electrolytic capacitor and the boost-up reactor, the

remaining part of the proposed circuit is constructed only of

silicon components, namely, IGBTs and diodes. As a result,

the proposed circuit is highly efficient and highly reliable.

Simulation and experimental results clearly demonstrate that

the circuit is capable of providing sinusoidal waveforms for

the input and output, and high efficiency and a high power

factor can be achieved.

II. PROPOSED CIRCUIT TOPOLOGY

Fig. 2 shows the proposed circuit configuration. The

IMC

can be simply divided into primary and secondary stages.

The

primary stage for the ac power source consists of 12 units of

reverse-blocking IGBTs [15], also known as a current-

source

rectifier,where bidirectional power flow is possible in this

circuit

structure. A LC filter is required at the input of the primary

stage

to smooth the input current. The secondary stage for the

motor

consists of six IGBT units, which is similar to a standard

voltage source inverter. The advantage of this converter over

a BTB is

that the primary side does not contain switching loss

because zero-current switching can be applied. The

switching timing of

the primary side is during the zero-current period of the dc-

link

when the secondary stage output zero voltage. Therefore,

high

efficiency is achievable in this converter [11].

The other reason to use the IMC is that the IMC has a dc-

link mpart, which is different than the conventional matrix

converter. The dc-link part is utilized by adding a boost

converter to the IMC. The boost converter connects to the

battery and the other

terminal of the battery is then connected to the neutral point

of

the motor. A snubber circuit is also included in the dc-link

part to absorb the voltage overshoot from reactive elements

in the circuit [16]. It is used to prevent damage to the

switching devices in the secondary side due to a sudden

large voltage. It should be noted that the capacity of the

snubber capacitor is smaller than the dc-link capacitor in a

BTB system, because the ripple current of the dc-link part

does not flow in the snubber capacitor. The chopper circuit

is connected in the dc link and batteries are connected to the

neutral point of the motor. The leakage inductance of the

motor is used as a boost-up reactor in the proposed circuit.

As a result, the proposed converter does not

require bulky passive components.

Fig. 3(a) shows a control block diagram of the proposed

circuit.

The primary side, the dc chopper, and the secondary side are

individually controlled by their own commands. A carrier

comparison method is used as the PWM modulation,

according

to the control strategy [17]. The relationship between the

output

and input voltages is obtained by (1). The secondary side

operatesas a four-phase voltage-source inverter by addition

of thedc chopper as the fourth leg

where sxy represents the switching function of the switches.

When sxy is turned ON, sxy = 1, and when sxy is turned OFF,

sxy = 0.

A. Primary-Side Control

The primary-side controller is designed with a current-

type

PWM rectifier command. It uses a pulse-pattern conversion

to

convert the PWM pulses of the voltage source type into the

PWM pulse of the current source type by a simple logic

selector.

It uses a single-leg modulation where the switching period

can be reduced from 2π/3 to π/3, where the 2π/3 is the

switching

period of the conventional two-phase modulation [15]. That

is, the leg with the maximum input phase voltage will

always be

turned ON, and the other two legs will be always turned

OFF,

as shown in Fig. 3(b). When the maximum input phase

voltage

Sree Vardhan IJECS Volume 2 Issue 11 November, 2013 Page No. 3250-3255 Page 3252

is changing, (for example, from +R-phase to −S-phase), the

related max phase voltage leg and the mid phase voltage leg

will

be switched at zero current until the relevant switch that

contains

the mid phase voltage becomes the maximum input phase

voltage. From this direct conversion technique, a dc-link

voltage

that contains a ripple with six times of the input frequency

will

be formed [15].

B. Secondary-Side Control

A conventional controller method for a voltage-source-

type

inverter is applied to the dc chopper and the inverter with a

lean

controlled carrier modulation. The carrier modulation forms

a

Fig. 3 (a) Control block diagram. (b) Primary-side-switching

pattern

new carrier, where the peak position of the triangular

carrier

is controlled by the duty ratio of the rectifier-side pulse. This

rectifier pulse is used to control the switching timing of the

primary stage and the zero-vector of the secondary stage.

From

the control, zero-current switching is achieved in the

primary

stage, where the dc-link current becomes zero at the peak of

every carrier. This new carrier is then used in the secondary

side

and the dc chopper side as a normal PWM comparison

method,

also referred to as an inverter carrier.

The boost converter is not a stand-alone circuit in the

proposed circuit. Operation is strongly dependent on the

secondary side of the IMC. Zero-vector outputs on the

secondary side are the key factor to link the boost converter

to the IMC. The zero vector controls the amplitude of the

output voltage. There are two functions of the zero-vector

output to the secondary side. The first is to implement zero-

current switching on the primary side so that the switching

losses do not occur at the primary side. The second function

involves operation of the boost converter, which will be

described in a later chapter.Fig. 4 shows an example of the

relationship between the normal carrier applied to the

primary side and the new inverter carrier applied to the

secondary side.

The inverter commands are given by the voltage controller

as described in Chapter IV. It is noted that the dc chopper is

controlled as the fourth leg of the inverter so that the dc

chopper command is compared by the same carrier with the

inverter voltage commands. There are two methods to

generate an inverter carrier; Fig. 4(a) represents the

symmetrical type, which has approximately double the

switching frequency of the rectifier switching frequency,

and Fig. 4(b) shows the asymmetrical type, which has the

same switching frequency as the rectifier switching

frequency [16]. min Fig. 4(a), the bottom peak position of

the triangular carrier is controlled by the duty ratio of the

rectifier pulse, as shown in

.

Fig. 4. Relationship between the zero vectors and boost converter

operation. (a) Symmetrical inverter carrier. (b) Asymmetrical inverter carrier

the upper part of the figure. The chopper commands, along

with

the inverter output voltage commands, are compared with

this

new inverter carrier to obtain the desired switching patterns.

The

zero-vector periods are shown in the lower part of Fig. 4(a).

The

switching pulses of the secondary side attain the zero

vectors

for every carrier cycle. The primary side arms switch at

every

zero-vector period.

In Fig. 4, zv_u and zv_l represent the zero-vector periods of

the inverter, where zv u = Sup = Svp = Swp = 1 (upper arm

zero vector) and zv l = Sup = Svp = Swp = 0[lower arm zero

vector (Sun = Svn = Swn = 1)]. The upper arm of the chopper

(Scp) switches ON at every zero-vector period of zv_u. On

the

Other hand, the lower arm of the chopper (Scn ) will switch

ON

Sree Vardhan IJECS Volume 2 Issue 11 November, 2013 Page No. 3250-3255 Page 3253

at every zero-vector periods of zv_l. During these zero-

vector

periods, the boost converter is operated in the ON-state, and

the battery current through the leakage inductance of the

motor

increases. During the nonzero-vector periods, also known as

the OFF-state operation, the battery current is released into

the

capacitor in the LC filter at the power source. The operation

state in the figure is referred to the boost converter

operation.

When the switching frequency of the rectifier is 10 kHz, the

control method applied in Fig. 4(a) generates a new

symmetrical

carrier that has a frequency of approximately 20 kHz. This

is approximately twice the primary-side switching

frequency.

Alternatively, according to Fig. 4(b), an inverter carrier can

be

formed based on the duty of the rectifier command, which is

asymmetrical with a frequency of 10 kHz

By comparing the symmetrical and asymmetrical

inverter carriers in Fig. 4, it should be noted that the zero-

current n switching in the rectifier is not affected by the

inverter carrier because

both carriers are formed following the rectifier duty. Since

every

carrier time is longer in the asymmetrical inverter carrier,

the

sequence of the zero-vector periods becomes slower;

therefore,

the boost converter will achieve better efficiency, but the

current

ripple in the battery will be increased. Further, the

asymmetrical

method can achieve better total harmonic distortion (THD)

values for the output because the deadtime effect is smaller

due

to the lower switching frequency. The other disadvantage of

the asymmetrical inverter carrier is the detection of the load

current. Usually, the average value of the load current

appears at the peak of the symmetrical inverter carrier so

that it can be easily detected using the symmetrical inverter

carrier. However, for the asymmetrical carrier, the average

current point does not agree with the peak of the

asymmetrical carrier; therefore, in order to detect the

average current, a lowpass filter is required. Consequently,

control performance will be decreased.

IV. UTILIZATION OF THE NEUTRAL POINT OF THE MOTOR

The voltage commands of the secondary stage are decided

by the battery current command and the output voltage

commands for the three-phase load. A three-phase inverter

has eight output voltage space vectors, including two zero

vectors. The importance of the zero vectors explains the

behavior of the boost converter along with the neutral point

of the motor. The boost converter will operate at every zero

vector of the secondary side of the converter. On the other

hand, the output voltage for the three-phase load is

controlled by other voltage vectors, as shown in [14]. Fig. 5

illustrates the output current-flow diagram of the secondary

side under the normal operation and Fig. 6 shows the zero-

phase-sequence equivalent circuit, where the battery is

operating at discharge mode. In Fig. 5, the secondary side

functions as a conventional three-phase inverter with a

motor; it controls the motor speed and torque. Zero-phase

sequence is happening at every zero-vector periods of the

secondary side. The current at the neutral point of the motor

is zero and a positive or negative battery current can be

controlled, as shown in Fig. 6. Note that

Fig. 5. Secondary-side current flow diagram (normal operation)

the polarity of the battery voltage can be connected in facing

the neutral point of the motor or in a reverse way [14]. Cin

represents the capacitors from the LC filter; since two

switches in the primary side will always be turned ON, the

capacitors Cin

can be considered in the dc-link voltage. On the other hand,

for

the zero-phase sequence, the motor line voltage can be

considered as zero so that the motor can be considered as a

leakage inductance. In addition, the secondary side of the

converter can be considered as a single-leg topology.

. The battery current first goes into the secondary side and

flows out through the neutral line and charges or discharges

the battery. The battery current can be controlled by the

proportional–integral (PI) controller. The zero vectors are

two particular vectors that generate zero line voltage to the

motor. The neutral-point voltage v0 of the motor, based on

the neutral

point of the dc-link part, is obtained by the following

equation:

Vo= Edc/2 When all upper arms are ON

v0 =−Edc/2 When all lower arms are ON (3)

where Edc is the dc-link voltage and v0 is the voltage of the

neutral point of the motor, based on the neutral point of the

dc-link part. A high dc-link voltage is mandatory in order to

control the zero vectors; therefore, the relationship between

the dc-link voltage (Edc), the inverter line voltage (vinv ), and

the battery voltage (Vbat ) will be discussed. The inverter

output voltage, vu , vv , and vw , with respect to the neutral

point voltage of the

Sree Vardhan IJECS Volume 2 Issue 11 November, 2013 Page No. 3250-3255 Page 3254

dc link, is expressed as

vu = aEdc/2sin ωt + v0

vv = aEdc/2(sinωt − 2π3)+ v0

vw = aEdc/2(sinωt − 4π3)+ v0 (3)

where a is the modulation index of the motor phase voltage,

0 <

a < 1, v0 is the neutral point voltage of the motor (during

zero

phase sequence), and ω is the inverter output angular

frequency.

The inverter line voltage is then given by (u–v phase)

vuv = a√3/2 Edc sin_(ωt + π/6) (4)

Equation (5) shows the relationship for an inverter to obtain

the maximum output line voltage Vinv (rms) under the

maximum

reference magnitude of a three-phase modulation

Edc ≥ 2√2 /√3Vinv . (5)

The maximum line voltage between the inverter leg and

chopper

leg can be obtained as (rms)

vux =√2/ √3Vinv + Vbat (6)

Since vux must be smaller than Edc, the inverter voltage and

battery voltage are constrained by the following equation

Edc >√2/ √3Vinv + Vbat (7)

As a result, the dc-link voltage of the proposed circuit must

satisfy both requirements as shown by the following

equation,

which can be referring to Fig. 6

Note that in (8), the Vbat can always be neutralized with half

of the Edc under the two conditions. That is, Vbat must be

always

smaller than half of the Edc, since the Edc is always known

as

the 0.866 of the input phase voltage, as shown in the

following

equation

√2/2 Vin0.866 > Vbat (9)

Furthermore, a new expression of the secondary-side

current

is given as follows, assuming that the leakage impedance is

even

during the zero-phase-sequence equivalent circuit

iu = ia + ibat/3 iv = ib + ibat/3 iw = ic + ibat/3 (10) where iu , iv , and iw are the inverter currents, ia , ib , and ic are

the

positive-phase-inverter current, and ibat is the battery current

V. SIMULATION RESULTS

Table I shows the simulation parameters for both results.

The

proposed circuit was simulated under two conditions of

battery

discharge and charge. An automatic current regulator (ACR)

ncontroller controls the battery current to a desired positive

or negative value. An ideal battery current ibat is purposely

adjusted

at a specific time of 38 ms to confirm the proposed circuit

performance. The motor model, which consists of three sets

of

voltage sources as back-electromotive forces and leakage

inductances, is used in the simulation. The asymmetrical

inverter

carrier was used in the simulation. Fig. 7 shows the battery

discharge mode, with the battery current controlled from 0.5

to 2 A. The two waveforms show the input power supply

voltages vr , vs , and vt , the input currents ir , is , and it , and

the output line voltages (vuv(LPF) , vvw(LPF) , and vwu(LPF) )

through a low-pass filter, which has a cutoff frequency of 1

kHz, to observe the low-frequency components, the output

currents iu , iv , and iw , and the battery current ibat . The

results show that the THD of both the input and output

currents are less than 4%. It should be noted that at 20 ms,

the input current magnitude decreases due to the increment

of ibat , which indicates that the increase of the battery power

leads to a decrease in generator power. On the other hand,

Fig. 8 shows the ACR controlling the battery current from

0.5 to −2 A. The battery is charged from a generator under

this condition. The results also showed that when in the

charging mode, both the input and output currents have

good sinusoidalwaveforms. At 20 ms, as the ibat decreases,

the input current is forced to increase, because higher power

is required to charge the battery. These two waveforms

provide evidence of good power management between the

generator and the battery.

i/p voltage,i/p current,o/p voltage,o/p current,battery current

Sree Vardhan IJECS Volume 2 Issue 11 November, 2013 Page No. 3250-3255 Page 3255

Fig. 7. Simulation results (battery = discharge mode).

i/p voltage,i/p current,o/p voltage,o/p current,battery current

Fig. 8 Simulation results (battery = charge mode)

VII. CONCLUSION

A new control method is proposed by utilizing the neutral

point of a motor and connection to an IMC for motor drive

applications. Control over the inverter zero-vector periods

allows an additional chopper leg to perform as a boost

converter

with connection to the neutral point of a motor. Simulation

results demonstrated good sinusoidal waveforms and

confirmed the validity of the proposed method.

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